Japanese Patent No. 3627719 discloses one of thermoelectric modules that have been known. The thermoelectric module device contains, therein: thermoelectric elements such as in-series multiple Peltier elements; an upper substrate bonded to the thermoelectric elements; and a lower substrate arranged facing the upper substrate and bonded to the thermoelectric elements. The lower substrate has two surfaces, a first surface facing the upper substrate and a second surface positioned on the other side of the upper substrate. The first surface of the lower substrate is bonded to the thermoelectric elements and is mounted with electrodes for supplying electric current to the thermoelectric elements.
The second surface of the lower substrate is provided with a metallization layer via which the lower substrate is mounted on a package (case) by soldering. The lower substrate includes a junction bonded to the thermoelectric elements and a power supply portion mounted thereon with the electrodes. The thermoelectric elements connect the junction of the lower substrate to the upper substrate.
Upon mounting the thermoelectric module device onto the package, pre-soldering is occasionally implemented, by which solder is bonded to the metallization layer of the lower substrate beforehand, in order to simplify a mounting operation. During the pre-soldering process, the thermoelectric module device, which has the upper substrate, the lower substrate and the thermoelectric elements, is compelled to receive heat. In such circumstances, the lower substrate may distort due to a possible large difference in coefficient of thermal expansion between a coefficient of thermal expansion of the soldering material and the one of the lower substrate. Here, stress may be applied to the junction of the lower substrate or to the thermoelectric elements per se.
Especially, the power supply portion of the lower substrate, which is not connected to the upper substrate, is inferior in rigidity to the junction of the lower substrate, which is connected to the upper substrate. This structure of the thermoelectric module causes distortion in the power supply portion more than in the junction of the lower substrate and can apply an excessive amount of stress to the junction between the lower substrate and the thermoelectric elements.
The present invention has been made in view of the above circumstances and provides a thermoelectric module device in which stress applied to thermoelectric elements is reduced.